1. Field of the Invention
Embodiments of the present invention relate to a drawing apparatus configured to perform drawing on a substrate with a plurality of charged particle beams.
2. Description of the Related Art
In a drawing apparatus configured to perform drawing on a substrate with a plurality of charged particle beams, non-uniformity in characteristic among the plurality of charged particle beams becomes an issue. As this non-uniformity, specifically, a locational error or angular error of each charged particle beam, and the like can be exemplified. This non-uniformity is disadvantageous in terms of the overlay accuracy of the drawing apparatus.
As a method of compensating for the corresponding non-uniformity, there is a method discussed in Japanese Patent No. 3803105. This method shifts the position of each aperture of an aperture array or a lens array, which is in front of a projection optical system, according to the aberration of the projection optical system, thereby intentionally making non-uniformity in the positions and angles of charged particle beams entering the projection optical system. Further, the shift amount of each aperture of the aperture array and the lens array is determined such that the corresponding non-uniformity negates non-uniformity among the plurality of charged particle beams occurring by the aberration of the rear-side projection optical system. In this way, the final non-uniformity among the plurality of charged particle beams is compensated for.
However, the shift amount of each aperture is limited. This limit will be described with reference to FIG. 3. In a case where an amount of aberration of a rear-side projection lens 125 is large, and a shift amount of each aperture 201 which is to be given on the front side of the projection lens 125 is large, as illustrated in FIG. 3, some charged particle beams are reflected at a converging lens array 119. In other words, compensation that is made by shifting the apertures 201 is limited according to vignetting at the converging lens array 119, and can be made only within a range that is not limited by the corresponding vignetting.
In the case of compensating for not only non-uniformity according to aberration of a projection system but also non-uniformity according to aberration of an optical system (charged-particle optical system) by shifting apertures, there is a compensation limit according to vignetting of charged particle beams at an optical element. However, any method of solving the issue of the compensation limit has not been discussed.